The present invention relates to electrical generators having bearings for the rotor at opposite ends of the generator enclosure and particularly relates to apparatus and methods for isolating the bearing housing from the interior of the generator enclosure to preclude oil leakage into the generator.
Electrical generators are constructed with bearings for the rotor at opposite ends of the generator. Typically, one side of the bearing housing is partially enclosed by the generator enclosure and an opposite side of the bearing housing lies partially outside of the generator enclosure. Thus, approximately half of the bearing housing along the inside of the generator enclosure is exposed to the high suction pressure of a generator fan used for cooling the rotor. The other half of the bearing housing located outside the generator enclosure is exposed to atmospheric or ambient pressure. The oil in the bearing itself, which could be a tilt pad bearing or a plain journal bearing, is thus exposed to the high suction pressure and ambient pressure on opposite sides of the bearing housing. With the interior of the generator enclosure being at negative pressure, oil from the bearing can and does leak into the generator enclosure contaminating its interior. For example, oil leakage into the interior of the generator coats the internal surfaces of the generator with oil and compromises generator performance. Oil is also a magnet for dirt and dust which likewise compromises performance.
In prior generators of this type with half of the bearing housing exposed to interior vacuum pressure and the other half exposed to ambient pressure, a dedicated vapor extractor is typically provided to overcome the high suction pressure of the main generator internal cooling fan. That is, the pressure generated by the vapor extractor fan and the main generator fan are roughly comparable. Thus by providing a vapor extractor coupled to the bearing housing for example adjacent the internal oil deflector, oil vapors may be extracted from the bearing housing without leakage flows into the generator enclosure. Also, it will be appreciated that the vapor extractor requirements for the generator bearing housing are much higher than the requirements for the vapor extractor associated with the lubrication oil system typically applied to the generator bearing. Thus the two systems cannot be combined into one. Further the necessary vapor extractor requires precise setting of the vacuum and high maintenance for the system to operate satisfactorily. Because large quantities of oil vapor are drawn through the vapor extractor, frequent changes of filter media are also required. A system malfunction and vapor extractor motor overload with potential for shortening its life expectancy and premature failure can be predicted if maintenance is not performed as required.
In addition, the oil drain pipe on the bearing housings has been located at an elevation with respect to the bottom of the bearing cavity such that the high suction in the bearing housing will raise the oil level in the housing higher and above that necessary to drain the bearing cavity. This will cause backups and oil leaks into the generator past the oil deflectors. To remedy that situation, additional piping has been provided to apply an opposing vacuum on the bearing housing drain pipe.
In accordance with a preferred embodiment of the present invention, there is provided a generator bearing housing isolated from the interior of the generator enclosure thereby enabling the bearing housing to lie wholly at ambient pressure while also enabling removal of oil vapors from the oil bearing cavity. To accomplish the foregoing and rather than physically relocating the bearing and bearing housing, the low pressure region within the generator enclosure is isolated from the bearing housing by creating a seal between the rotor and the end wall of the generator enclosure sealing between the low pressure region within the generator enclosure and ambient pressure outside the enclosure. This isolation of the bearing housing and the generator enclosure may be created by extending the end wall of the generator enclosure axially inwards and providing a seal, for example labyrinth seal teeth about the rotor. Consequently, the vacuum pressure within the generator enclosure is eliminated from the bearing housing. Any oil that may pass the inner oil deflector may accumulate in the lower portion of the deflector and drain back into the bearing cavity.
It is still important, however, to remove oil vapors from the bearing cavity to preclude those vapors from escaping from the housing. To accomplish this, the vapor extractor typically utilized with the oil lubrication system and which applies nominal vacuum pressure slightly below ambient pressure is used to suction the oil vapors from the bearing cavity. This eliminates the need for the vapor extractor which necessarily had to operate at low vacuum pressures comparable to the pressures within the generator enclosure to remove oil vapors from the bearing cavity. Additionally, the bearing housing drain pipe is relocated to a lowest possible elevation to reduce the amount of oil that accumulates in the bearing housing before it starts to drain out and thus the oil level is maintained as low as possible.
In a preferred embodiment according to the present invention, there is provided an electrical generator comprising a generator housing having a wall at one end of the generator, a rotor within the housing, a bearing at the one end of the generator for supporting one end of the rotor, the end wall including an axially inwardly directed cavity locating the bearing outside the generator housing and under ambient pressure.
In a further preferred embodiment according to the present invention, there is provided an electrical generator having a generator housing, a wall at one end of the housing, a rotor within the generator housing and extending through the wall at the one end of the housing, a lubrication oil system for the generator including an oil vapor extractor and a bearing for supporting the rotor adjacent the one end of the housing, a method of minimizing or eliminating oil leakage from the bearing into the generator housing comprising exposing the entire bearing to ambient pressure and employing a vapor extractor provided with a lubrication oil system to apply low suction pressure to the bearing cavity to withdraw oil vapors therefrom.
In a further preferred embodiment according to the present invention, there is provided in an electrical generator having a generator housing, a wall at one end of the housing, a rotor within the generator housing and extending through the wall, a fan within the housing for applying a high pressure suction to cool the rotor, and a bearing housing including a bearing for supporting the rotor adjacent the one end of the generator housing and lying partially within the generator housing at generator fan high suction pressure and partially outside the generator housing at ambient pressure, a method of minimizing or eliminating oil leakage from the bearing housing into the generator housing comprising the steps of isolating the bearing housing from the high suction pressure of the generator fan by providing a seal between (i) the rotor adjacent the one end thereof and at a location axially inwardly of the bearing and (ii) the end wall thereby exposing the entirety of the bearing housing to ambient pressure.